1. Field of the Invention
The present invention relates to a cleaning mechanism of a corona discharging apparatus of an electrophotographic printing apparatus.
2. Description of the Related Art
In the corona discharging apparatus (charger) for use in the electrophotographing method, a method in which the high voltage is applied onto a tungsten wire onto which the predetermined tension is applied, and by the corona discharge generated thereby, the photoreceptor surface is charged, is used. The surface of the corona wire is coated by gold, platinum, or oxide film, however, by ozone generated by the corona discharge, the oxide such as SiO2 is generated on the corona wire surface, or the toner scattering in the apparatus adheres to the surface. As described above, when the surface of the corona wire is stained by products or toner, because the corona discharge generated from the portion becomes uneven, thereby, unevenness (charge unevenness) is generated in the photoreceptor potential.
Recently, in a laser printer, an increase of minuteness and image quality is required, and the longitudinal streak caused by the charge unevenness is a fatal defect in the printing quality. Accordingly, conventionally, a corona wire cleaning mechanism by which cleaning of the corona wire is automatically conducted at the predetermined timing based on number of printing pages or the operating time, is well-known.
In the conventional method, a screw shaft is passed through a cleaning member in which a female-screw is tapped, and the screw shaft is rotated for a predetermined time by a small sized motor, thereby, the drive power in the axial direction is transmitted to the cleaning member. When the cleaning member is moved from an initial position of the motor to the opposite side, a wiper attached to the cleaning member cleans the corona wire. The cleaning member reversely rotates the screw shaft after a predetermined time, and operates the screw shaft so that the cleaning member returns to the initial position. The movement time of the cleaning member from the initial position to the opposite side differs because the load is changed according to the stained condition of the surface of the corona wire. There is a case where the cleaning member returns without arriving at the opposite side when the rotation time margin of the screw shaft is small. In such the case, because a portion that the cleaning of the corona wire is not conducted, is generated, it is forced to have the large rotation time margin of the screw shaft. However, because the screw shaft is rotated for a predetermined time, the rotation is continued also after the cleaning member reaches the turning point. Accordingly, the motor is continued to have a load thereon, therefore, by the deformation of a gear and deviation of the shaft, the gear is meshed-in and locked. Accordingly, when the load is light and the movement time to the opposite side is short, the locked time of the motor is long. When it comes to this condition, it is forced to replace the charger or transfer device by a unit, therefore, there is a problem that the maintenance requires a cost.
An object of the present invention is to prevent the generation of the lock by making the load applied on the motor smaller than a predetermined value by providing a torque limiter function to the cleaning member, and to make the cleaning member stably conduct the cleaning operation, and to improve the life of the corona discharging apparatus.
The above object can be attained, by releasing the load more than a predetermined value by using a wire spring-like member having the torque limiter function for a cleaning member to conduct the power transmission of the screw shaft, the deformation of the gear and the deviation of the shaft are eliminated, and, by preventing the generation of the lock of the motor.